Each year, more than 13,000 children in the United Stated are diagnosed with type I diabetes (T1D), in which autoimmune destruction of the pancreatic islets results in loss of endogenous insulin production. The current standard of care for these patients is insulin therapy, which restores glucose homeostasis and aims to prevent complications associated with hyperglycemia. However, new therapies to halt the autoimmune destruction of the islets could be useful because it has been demonstrated that the damaged islets can regenerate if immune tolerance is reestablished at the time of diagnosis of hyperglycemia. I propose to study methods using gene therapy vectors to make therapeutic cells in order to treat T1 D. I have tested DC infected with adenoviral vectors expressing several different transgenes, including FasL, IDO, IL-10, as well as a soluble and membrane-bound form of IL-4 (slL-4 and mblL-4), for their ability to delay onset of diabetes in 10-12 week old female NOD mice after intravenous adoptive transfer of a million cells. I have similarly screened 1 ug of exosomes, which are small membrane-bound vesicles, produced by these modified DC. My preliminary results indicate that administration of DC expressing slL-4 are capable of completely preventing disease onset, whereas a single treatment of exosomes expressing mbll_-4 delays diabetes onset by approximately 5 weeks. The goal of this research is to optimize the therapeutic potential of DC and DC-derived exosomes which have been engineered to be tolerogenic using adenoviral vectors expressing either slL-4 or mblL-4 for the treatment of T1 D, and to understand the mechanisms by which these DC and DC-derived exosomes exert their therapeutic effects. To this end, I propose to optimize these preliminary results, treating 12-week-old NOD/ShiLTJ mice with adoptive transfer of either DC-derived exosomes or parental DC that have been modified to express either slL-4 or mbll_-4. I will first determine the most effective treatment schedule, and then I will determine the most efficacious dose. After optimizing the dosing of DC and DC-derived exosomes for the prevention of diabetes onset, I will determine if this treatment schedule is effective at reversing established T1 D. I hypothesize that adoptive transfer of IL-4 transduced DC or their exosomes protects against T1D by modulating the function of endogenous T cell subsets. Since IL-4 seems to be effective I will first examine the effect of our DC and exosome therapies of Th1/Th2 balance in the NOD mouse, and then will conduct adoptive transfer studies into NOD/Scid mice as well as FACS and ELISPOT to see if the treatments are capable of generating a regulatory T cell population.